[PATCH] rbtree: rust: add RBTree::is_empty

[Alice Ryhl <aliceryhl@google.com>]

In Rust Binder I need to be able to determine whether a red/black tree
is empty. Thus, add a method for that operation to replace

	rbtree.iter().next().is_none()

This is terrible, so add a method for this purpose. We do not add a
RBTree::len method because computing the number of elements requires
iterating the entire tree, but checking whether it is empty can be done
cheaply.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/kernel/rbtree.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index 8d978c8967475cc2631b50721798f7e8cd1551fd..9457134eb3afdf7a214a28fcbe2e6b8065cc9a86 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -191,6 +191,12 @@ pub fn new() -> Self {
         }
     }
 
+    /// Returns true if this tree is empty.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.root.rb_node.is_null()
+    }
+
     /// Returns an iterator over the tree nodes, sorted by key.
     pub fn iter(&self) -> Iter<'_, K, V> {
         Iter {

---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250616-rbtree-is-empty-28f51fccb99a

Best regards,
-- 
Alice Ryhl <aliceryhl@google.com>